Compact filtration units are well known. One such unit is a blood filter, comprising a multi-piece, rectangular housing with coaxial fluid connections, the connections being separated from each other by a multi-layered, pleated filter element so as to permit a fluid to be filtered to pass from inlet to outlet only by flowing through the filter element. The filter element at each of the two protruding ends is clamped between two specially designed wall components of the top and bottom housing components and welded thereto. The filter element is also secured at the two outer sides by a sealant.
German Patent No. 24 44 224 C3 also discloses a filtration unit with a pleated filter element, comprising five aligned plate-shaped components. The filter element is supported on the filtrate side by means of a porous carrier that has ribs which extend into the pleat folds. The pleated filter element is further supported by sections of the central plate-shaped components, to which the filter element is cemented at its sides so as to render it fluid-tight.
The drawbacks of such prior art devices are their large number of components and the existence of areas in which the individual components of the filtration unit are so tightly bound to each other that fluid flow is restricted. In addition, such devices are difficult to fabricate because of their complex construction, and the multiplicity of fluid-tight connections present more potential leakage points, often leading to premature breakdown of the filter units during operation. A still further disadvantage is that such filter units possess a relatively large dead space between the filter element and the housing components. This is undesirable in the cases of toxic and highly refined, costly materials. Finally, the pleated filter elements, which have either no support or support on one side only, can be distorted by fluctuations in fluid pressure or by back flushing.
There is therefore a need in the art for a fluid filtration unit having a single filter element which will withstand pressure fluctuations and back flushing, that is made of a small number of components and that has a minimum amount of dead space. These needs are met by the present invention, which is summarized and described in detail below.